Effects of feldspar and salinity on the mineral sequestration capacity of CO2 in high-salinity aquifers

Mineral sequestration of CO2 is considered to be the safest mechanism in the long-term storage of CO2 in deep saline aquifers. This study aims to investigate the effect of feldspar and salinity on the mineral sequestration capacity of CO2 in deep high-salinity brine aquifers by taking Jiangling Depression of Jianghan Basin for instance. Numerical simulation on the long-term geochemical reaction and transport was performed by taking TOUGHREACT as the simulation tool. Simulation results indicate that the effect of feldspar on the mineral trapping capacity of CO2 does not depend on the total content of feldspar, but depends on feldspar type and relative content. With Mgrich minerals such as chlorite or dolomite present, the mineral composition abundant in K-feldspar is less favorable for the mineral sequestration capacity of CO2 for the reason that a large amount of illite precipitates, consuming a lot of Al3+ in the aqueous solution, thereby limiting the precipitation of dawsonite, especially for the high-temperature sedimentary environment. In addition, the effect of salinity on the mineral sequestration capacity of CO2 represents two aspects: one for the longer migration distance due to the lower solubility of higher salinity and the other for CO2 mineral trapping capacity per 1 m(3) medium which is not in simple decreased with salinity, depending on K-feldspar present or not. For the mineral composition with K-feldspar present, CO2 mineral trapping capacity decreases with salinity, while with albite instead of K-feldspar, it increases with salinity owing to more precipitation of dawsonite.